Analog and digital circuits are used in countless varied applications, and are being integrated even more with each passing year. Prefabricated components and chips lie at the heart of most of these circuits. As these circuits have become not only more prevalent but also more complex, it has become increasingly important to those who manufacture and sell the component parts, as well as to those who purchase components and implement circuits using them, that secure and efficient methods be available to package and transport these often delicate or sensitive components. In addition, similar demands exist with respect to other electrical and mechanical components. Component suppliers traditionally ship their parts to the end user in various forms of transport packaging, the most popular being waffle trays or tape-and-reel arrangements. In tape-and-reel arrangements, the tape is thermoformed with a series of pockets formed along its length. A component part is inserted into a pocket and covered with a cover tape which secures the part inside. The cover tape is usually a film or web with a thermally-activated or pressure-sensitive adhesive deposited on its underside. A length of the carrier/cover tape combination is then spooled onto a circular shipping reel. This system provides an efficient arrangement in which the components can be packaged, shipped and presented to an automated assembly process.
Waffle trays are similar, except the pockets are provided in a grid pattern on a thermoformed tray. Instead of rolling the carrier onto a reel as with the tape, the trays are stacked for shipping and storage.
Circuit components are generally formed of a main body with terminals extending from near the edges of the main body. The main body is generally more robust than the terminals, and able to withstand forces typically encountered in shipping and storage. The terminals, however, are often quite delicate, and therefore, cause the most concern in shipping and storage. Any impact between a terminal and the interior of the carrier tape pocket, for example, can be potentially damaging to the component. Therefore, it is desirable to separate the component terminals from the inner surfaces of the pocket and to maintain that separation. To create the separation, a typical pocket includes a "pedestal" that holds the component off the bottom surface of the pocket. To maintain the separation, the pocket and pedestal must resist crushing during typical shipping and storage conditions.
The carrier is generally formed of a thin layer of thermoplastic, typically less than a millimeter thick. Because the pocket walls are so thin, the pockets are susceptible to being crushed when spooled onto a reel or stacked for shipping. The formation of the recessed pocket stretches the material even thinner in the side walls of the pocket, further reducing the strength of the pocket. Conventional efforts to increase the crush resistance of carrier pockets have centered around increasing wall thicknesses or changing the material. Unfortunately, increased thicknesses result in proportionate increases in shipping weight and cost, as well decreases in component capacity. Further, stronger materials are generally more expensive and/or heavier, which also increases production and shipping costs. Many tapes and trays have been fashioned from either high strength plastic or laminates of various plastics. These materials are more expensive than standard plastics, but do not significantly improve the overall pocket strength when used in typical industry thickness ranges.
In certain applications, it is desirable that the packaging materials conduct electricity or dissipate static in order to protect the component from electrostatic damage. In these cases, the resin from which the carrier is formed is generally impregnated with a carbon powder or the like. The presence of the carbon powder, however, tends to degrade the structural integrity of the plastic, and the design of a conductive carrier pocket must take into account the resultant loss of strength.
Some carrier manufacturers compensate for the resultant loss of strength by providing a laminate structure in which a more pure plastic structural layer is sandwiched between two thin carbon-impregnated layers. This approach does provide added strength, but has several drawbacks in addition to the increased production costs generally involved with producing such a laminate. The conductive qualities of the laminates are generally inferior. Further, the thin conductive layer can be stretched too thin in the forming process or scratched off the structural layer in use, either of which can diminish the electrostatic protection desired. Also, the three-layer structure under certain conditions, can store charge like a capacitor. Therefore, it is preferable to provide a single conductive layer and compensate for the reduced strength of the material in other ways.
As for the pedestal, conventional designs extend at steep angles from the pocket bottom and provide a flat support surface on which the component rests. One disadvantage of these typical designs is that the pocket and the pedestal strength depend almost entirely on the inherent strength and rigidity of the material. Further, these pedestals often have near-vertical sides that are even more susceptible to bending, buckling, or collapsing. The typical pedestal is not very resistant to compressive forces applied to the component from above or to the pedestal from below.
Examples of known carrier tape designs are shown in U.S. Pat. No. 5,265,723, to Chenoweth et al., and U.S. Pat. No. 5,152,393, to Chenoweth, each of which illustrate microchip storage tape having pockets for accommodating electronic components. In Chenoweth (which is incorporated by reference into Chenoweth et al.), a bottom wall has a plurality of linear, upwardly-projected, V-shaped ridges, the inclined inner surfaces of which lie at the edges of a center portion of the pocket and serve to keep the microchip centered. Rectangular, raised support shoulders with substantially parallel, vertical walls, extend diagonally across the corners of the center portion of the pocket between adjacent ends of the ridges. The shoulders, which are lower than the ridges, support the microchip, elevated above the bottom wall, with its leads extending over the ridges so that the leads do not engage the bottom wall or the ridges. While this pedestal arrangement serves well its intended purpose, maintaining the microchip in position in the center of the pocket, it does not account for the particular concerns addressed by the present invention.
Another example, U.S. Pat. No. 4,966,281, to Kawanishi et al., relates to an electronic component carrier tape with a number of cavities. In FIGS. 8a and 8b of this patent, the surface of a "valley" (between a "component-mounting portion" and a peripheral wall) of the cavity is corrugated with an angular pattern. Because the electronic component is bonded to the component-mounting portion, when the component is to be removed, bending strain will develop in the valley portion. The corrugations distribute this strain, increasing the resistance to bending. While the squared corrugations of this arrangement do somewhat improve the rigidity of the peripheral wall, stress can be concentrated by the corners of the corrugations themselves, which become points of potential failure.
Japanese Laid-Open Patent Application No. 8-198317, of Sakurai, and Japanese Laid-Open Patent Application No. 7-149393, of Takahashi, illustrate other examples of component carrier tape pockets with side walls reinforced by corrugation or patterning. U.S. Pat. No. 5,396,988, to Skrtic, illustrates a buttressed carrier tape pocket side wall, whereas U.S. Pat. No. 4,889,239, to Sandish et al., and U.S. Pat. No. 2,858,224, to Darrah, illustrate examples of other containers with side walls reinforced by corrugations or the like.
Rounded, as compared to squared, corrugations provide better stability by eliminating corners in which stress can be focused. However, if a flat component lead does contact the rounded inner surfaces of such a corrugation, the region of contact will be more focused than it would be with a flat wall, increasing the likelihood of damaging the component.
Thus, there is a need in the art for a component carrier pocket with a pedestal designed to better resist compression.
There is a further need for a component carrier with side walls designed to better resist compression.
There is also a need for a component carrier with side walls that resist compression but include regions that distribute impacts of the component leads.
There is an additional need for a component carrier incorporating each of these features, wherein the pedestal and the pocket side walls better resist compression, and the side walls include regions that distribute component impacts.